Scientists have developed a way to sterilise medical equipment without the need to use toxic chemicals.

The technique may also help in decontamination of biological warfare agents.

It makes use of the latest technology to create a 'cold plasma' which works at room temperature and at normal atmospheric pressure to kill off bacteria.

A plasma is a potent collection of electrically charged particles such as electrons, and non-charged particles, such as radicals.

E. coli before plasma treatment

It is usually created by super-heating a gas, and is referred to by some physicists as the fourth state of matter, the other three being solid, liquid and gas.

However, most plasmas at atmospheric pressure are thousands of degrees centigrade, and so are impractical for everyday use.

Researchers from Old Dominion University in Norfolk, Virginia, and the University of California in San Diego, have developed a way to solve this problem.

They created a 'cold plasma' by injecting a mixture of helium and oxygen into the gap between two electrodes supplied with a small amount of power.

Bacteria killed

They then found that exposure to the plasma killed two types of bacteria - Bacillus subtilis, which is similar to anthrax, and Escherichia coli, responsible for cases of food poisoning.

Damaged E. coli following treatment

The researchers believe the plasma may also kill more dangerous types of bacteria and viruses.

Although viruses have a different structure from bacteria, they would also become damaged by the charged particles.

Researcher Dr Mounir Laroussi said: "The use of cold plasma to sterilise heat-sensitive reusable medical tools in a rapid, safe, and effective way is bound to replace the present method which uses a toxic gas, ethylene oxide.

"Plasma is also being seriously considered for the decontamination of biological warfare agents."

Using plasmas to sterilise food packaging would also give the food a longer shelf life than at present.

The same technique could also be used on spacecraft leaving Earth to avoid transporting micro-organisms from Earth to other planets or moons.